US2577411A - Sequence and welding timer - Google Patents

Description

FIG. I

Dec. 4," 1951 D, P, FAULK 2,577,411

' SEQUENCE AND WELDING TIMER Filed Jan. 31, 1950 7 Sheets-Sheet 1 &

Dec. 4, 1951 D. P. FAULK SEQUENCE AND WELDING TIMER f7 Sheets-Sheet 2 Filed Jan. 51, 1950 INVENTOI? DONALD P FAULK BY Z A NEV Dec. 4, 1951 D. P. FAUI ..K

SEQUENCE AND WELDING TIMER '7 Sheefs-Sheet 3 Filed Jan. 51, 1950 INVENTOR DONALD P. FAULK AT 0 NEY Dec. 4, 1951 D. P. FAULK 2,577,411

SEQUENCE AND WELDING TIMER Filed Jan. 31, 1950 'I'SheetS-Sheet 4 F i -fififififi fi $3 I I III I g In I I s I i I l I s; i l I Ch I a 3 l N I I m (D \g fi I g W I I I I l I I l I I I I Wye/woe DONALD l2 FAULK E BY 8L 31M A TTD/ZNEY Dec. 4, 1951 D. P. FAULK SEQUENCE AND WELDING TIMER '7 Sheeis-Sheet 6 Filed Jan. 31, 1950 mSth INVENTOI? DONALD P FAULK Dec. 4, 1951 D. P. FAULK SEQUENCE AND WELDING TIMER '7 Sheets-Sheet 7 Filed Jan. 51, 1950 Sl70/I Si70/1 /NVENTO/? DONALD R FAULK BY w ATTOPNE V Patented Dec. 4, 1951 UNITED STATES PATENT OFFICE SEQUENCE AND WELDING TIlVIER Donald P. Faulk, Lexington, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application January 31, 1950, Serial No. 141,518

25 Claims. (01. 315-246) novel circuit arrangements, has succeeded in achievin these timing functions very accurately with a much smaller number of control relays and tubes than have heretofore been used for comparable functions. Such a drastic reduction in tube and relay requirements has also resulted in similar reductions in necessary wiring and in manufacturing time, thereby materially adding the additional advantage of reduced space requirements and manufacturing costs.

In addition to the above advantages, the invention makes use of a novel arrangement for synchronous operation with line voltage and is adapted for both synchronous and nonsynchronous operation, and for both pulsation and spotwelding at speeds substantially higher than heretofore possible. The embodiments adapted for synchronous operation are inherently full cycling. The embodiments adapted for pulsation welding automatically time only an integral number of "heat times. Self-compensatingfeatures in the system insure accuracy in sequence and weld timing despite poor line voltage conditions, temperature variations, or dust accumulation.

The invention achieves these advantages by providing generally a cascade arrangement of controlled-ignition gas-filled dischargedevices in sequence-timing circuits. The operation of each such device is dependent uponthe operation of the device preceding it in the cascade arrangement. A single switch in the circuit of the leading de vice thereby eifectively controls the termination of the operation of the entire cascade arrangement.

By providing two such discharge devices, each cascaded upon a single discharge device and a resistance in the path leading from the single to the two devices, an effective means for making the operation and therefore the functions of the two devices, dependent upon each other, is

provided. This desirable construction in. the present invention has been adapted for both synr chronous and nonsynchronous operation with ternating line voltage.

Peaking circuits for synchronizing operation with line voltage have been used to trigger gridcontrolled gas-filled discharge devices in novel.

arrangements of inverter operated circuits.

current source l2, as at points 20 and 2|.

tension spring 22 may be used to maintain the A novel arrangement of inductive coils with the sequence-timing circuits achieves simplicity in operation and economy in construction.

A permanent grid-biasing arrangement has also been provided for insuring stability of opviding a second embodiment of the invention adapted for synchronous spot-welding;

Fig. 3 is a schematic view of circuits for providing a third embodiment of the invention adaptable for nonsynchronous pulsation and spotwelding;

Fig. 4 is a schematic view of circuits for providing a fourth embodiment of the invention adapted for nonsynchronous spot-welding;

Fig. 5 shows curves illustratin the operation of Fig. 1;

Fig. 6 shows curves illustrating the operation of, Fig. 2;

Fig. 7 shows'curves illustrating theoperation of Fig. 3; and

Fig. 8 shows curves of Fig. 4.

Referring to the drawings in more detail, Fig. 1 shows a welding transformer Ill having a prialternating current source l2. Grid-controlled gaseous discharge devices, as, for example, thyratrons l5 and I 6, are connected for firing the ignitrons I3 and M, respectively, in a conventional manner as shown. An operator l1 may be arranged to provide a weld (and no weld) switching arrangement by providing contacts 18 and I9 on operator I! for selectively connecting or disconnecting thyratrons l5 and [6 from the The contacts I8 and i9 normally in the open position as shown. The operator I! may be closed by means of a core'23 in a solenoid 24 connected to ;a potential source andcontrolled by switch 24'.

illustrating the operation nected in parallel across the serieseconnected.

secondary 28 and rectifier 33. A triggering secondary 36 of a triggering transformer 311Wh$6roperation is to be hereinafterdescribed is, in'this instance, connected in series in the grid-biasin circuit 21.

Similarly, grid 38 of thyratron IE is normally held at a negative potential with respectxtocathode 39 by a grid-biasing circuit 40. The biasing c-ircuit k lll, has a -transformer-i secondary. M of transformer '2 fieconnected in series with a rectifying device 42 A smoothing capacitor 43; and ,re-: sistanee A41 are; connected ;in parallel across the serieseconnected rectifiier- 42 and; transformer secondary rl l This parallel-connected econstant potential source is connected across the cathode 39,-and -,gri-d 3B.- .-efp;thyratrcnxl6 inseries with a triggering I secondary- 45-of 2 the triggering transformer 31., Secondary; 4601? the welding trans-- iormerl 0 is connected across electrodes 41 and 48 of a type suitable for passing current through-a.

weld resistance load 49: One, of the terminals 41 is.opcratively-ponnected to: adevice 48' for-closingthe-terminals 4'1" and481-with'sufilcient pressure to subject the weld; resistances-load 49- :to squeeze load-, thereby producing -suitable welding con-tact. In -thi s:insta;nce, thedevioeABtis a valve arrangement for controlling, a-pressure source suchas air:

source fifi' The cp erator 55 risznormally held in the openposition bya tensiorrspring; l In this positiom: valve ;52::is; closedgandnseals "off I the air pressre source 49, and valve 53 is open, permitting escape of; air;pres sure-;fr omthegpressure-achamber fiiyabove the terminal ilathrouglrthe outlet 55: In this positiom the compressionspring 56lifts the term ina l t ll-awayriromgthei welding: load 46.

When the solenoid 51 is energized, operatorflill 'is caused; to, move .;to s. the left; thus; opening 3 the valve causinggairg, pressures; from the; pressure source 49' to force the terminal 41 downruponwthen welding -loadsi 49-:-at1=; a= proper; weld squeezing pressure. 51 is connectediby a;line:5i-:thr ough thesecondary Ear-of transformer EiL-whose. primary'fififi. is con-. nectedacross the al-ternating potential, source 12'; to the terminalfi L.

64 will normally leave terminals :6 l- :and 462 ;open

because ofthe :tension spring 5 A solenoidafi'o'r; fornloving the operator M-tothe left isiconnected.

w l sfii s nrlpoint 68. .Line 31 1is :main.- tained at a positiveapotential ,by a. constant lpo 52 and closing the valve 53, thereby;

One side of the energizing solenoid:

The; other side, of the energiz ing .;so,1.enoid 51 is connected-to the. terminal 162.; A contactor, 631,011 a sequence-initiating.operator 5 a ansformer]fi-iwhose. primary 1'! is:;con--:

nectedaacrossthealternatingicurrent source .1 2 any.

meanspf inesq-3 If :and ;32.,-:5 Mid-point 18 .nfitthe 7 ans ormer se ondaryii 15:;00nne0ted byixlin'a e'lfl si'st-ance 8Tto the negative potential line 69.

to the line 63 which is thereby maintained at a negative potential with respect to line 61. A smoothing capacitance 8% is connected across lines 61 and 69.

A snuffing condenser 8| in a stand-by and repeat circuit 82 has one of its sides connected throughpointiw and a" resistance 83 toiline 61. The other side of" the'snufiing condenser 3! is connected to line 84, one end of which leads through a resistance til to the positive potential line 6.1, and the. other end of which leads to anode 850i a controlled-ignition gas-filled discharge device suchas athyratron 35'. Cathode 86 of thyratron:,85 is-connected through line 86 and re- A gridrbiasingicapacitor 88 in series with a rectifying device 88' is also connected across the resistance '81 betivcen line 86 and the negative potential line 69. The off-time and repeat circuit 62 has aciditiona'lly -agriii-biasingv capacitor- 96, one side of which is connected to linePSA-and the other side of which isconnected to line 89 whichleads through repeat switch 89., resistance 91; potentiometer resistances-2 to one end of line 93, the other end of which .runs through variable contact arm 34 to potentiometer resistance 95 on voltage divider; line-3S; which is connected-between positive and negativepotential lines 61 I and 69: The same sidaof igrid-biasing capacitor 96- isalso connected through line-:89- toline-fllwhich runs: to anode'98:.-of a root ingdevice 39 having-w cathode. 566 connected to"point:l 62 on the voltage divider line 33-.- When a potential 1 first appears between lines SLandfiSirom source 51*, the positive potential iofzilineefil appears through resis tance 84 and lineal at anode of the off-time": and repeat circuit thyratronw85' and the'negative" potential of line 69 will appearthrough resistance 81 and line Beat thecathode-flfiwof thyratron'85 Therefore, as-soon-eas the cathode 86 is warm; thyratron 355 willbegin to conduct-through thee circuitconsistingrofline- 61, resistance 84, line: 84-, anode 85; cathode 86", line 66, resistance '81 to negativepotential linefis As soon as thyratron 85 begins; to conduct, a potential will appear: acrosszresistancefil between lines86 and 69 ythere by causingthe-grid-biasing capacitor 83 to charge: through rectifier .88 to produce a. normally nega tive :potential at point. I04 -with respect to the vpotential. of line'86x Control 'grid-zlfl5 ofthe thyra-' tron 89 is connectedxto -a line 106 rleadingufrompoint I04: Therefore, theegrid l05'willibecom'e negative with'respect to the cathode 8%" as soon 'as the thyratron-85 startsto conduct,and,' because of 1 the directional nature of the rectifyingdeVice-BB", willnormally 'remainznegative' with respect to the cathode 8G despite certain conditions to. be here matter 4 described. When the 'thyratr'on 85" con-- ducts; the: grid-biasing capacitors fl- 'willcharge so as wto-iacquirle azpositive potential on the side "89 and a negative potential on the side 84 by meansof :the circuiiiz consisting of positive potential line 61:: and 'portio'n of potentiometerresistance '95fad justable farmie 4; line" 93, 'potention1eter-resistance 92,;resistance 91-; repeat switch 89","line 89, capaci tance QilL L-line 84, anode-85,-cathode' 86 lineBSi resistance 81 and; negative'*:potentialline 69? However, the side-89 of' thegrid-biasing capacitance iwill- .bemaintained at a potentialonly slightly. positive with respect to 1 line 36' because the side 89 of condenser 9ii is also"connected through lineotlg line 91 andthe-rectifying device 99 to; point 152 on'-'the'-voltage divider line "96 Therefore, 1 the maximum positive 'pote'ntial' which the-side 39 of= condehser-avill chargeis approximately that of point I02 since the drop across the rectifying device 99 is small. Also when the thyratron 85 conducts, the snuffing capacitor 8I will charge with a positive potential at the point 68 with respect to 84 through the circuit consisting of positive potential line 61, resistance 83, point 68, snufiing capacitance 8 I, line 84, anode 85, cathode 86, line 86, resistance 81 and negative potential line 69. i

To start the sequence timer, a switch, as, for example," foot'switch I01, is depressed to close points I08 and I09 of the starter switch circuit I I which may consistof a solenoid I I I in series with the secondary II2 of a transformer 3, whose primary II4 may be connected across the alternating current source I2, and lines II5 and H6 running to terminals H1 and H8 controlled by contactor II9 of operator 64 in such manner that when operator 64 moves to theleft, terminals H1 and II 8 are closed and seal off the switch I01. When the foot switch I01 is depressed, current fiows in the starter switch circuit H0, thereby energizing the solenoid III and causing the operator I to move to the right against the force of tension spring I20 so as to cause a contactor I2I to open the line I22 and the contactor I23 to close the line I24 which has one end connected to point 66 and the other end connected to an anode I26 of a controlled-ignition gas-filled discharge device such as a thyratron I21 in a sequence-initiating circuit I25. Cathode I28 of the thyratron I 21 is connected through the line 86 and resistance 81 to the negative potential line 69. Since point 68 is connected through resistance 83 and solenoid 66 to the positive potential line 61, the potential between lines 61 and 86 will appear across the anode I26 and cathode I28. Also since grid I29 ofthyratron I21 is connected through resistance I30 and line 89 to the positive side of the grid biasing capacitor 90, the grid I29 will be slightly positive with respect to the cathode .I28 and the thyratron I 21 will, therefore, when switch I01 is closed, immediately begin to conduct current from positive potential line 61 through the sequence-initiating circuit I25, consisting of resistance 83, solenoid coil 66, point 68, line I 24. contactor I23, anode I26, cathode I28, line 86, resistance 81 to negative line 69. Since the drop in potential across the thyratron I21, when it conducts is relatively small, the potential of point 68 will suddenly drop to nearly the potential of line 86. Since the snuifing capacitance 8I cannot instantaneously discharge, the sudden drop in potential at point 68 will thereby cause the potential in line 84 and anode 85 to experience a large negative drop to a point below the potential of line 86 and cathode 86', thereby causing the current flow in thyratron 85' to be extinguished. This negative drop is shown in Fig. 5 at' the beginning of curve 85, which shows the potential of anode 85 with respect to cathode 86' whose potential is illustrated by curve 86'. Since, as already pointed out, the grid I05 of thyratron 85' is negative with respect to cathode 86', the thyratron 85' cannot again conduct, even after the snuffing condenser 8| has discharged, and the potential between lines 61 and 86 again appears across the anode 85 and cathode 86'. The moment the thyratron I21 is caused to conduct, current flows through the coil 66 causing the operator 64 to move to the left, thereby causing the contactor 63 to close the gap between terminals 6| and 62 so that current is made to flow from transformer60 toenergize the solenoid 6f 51.The operator is made thereby to'move to the left opening valve 52 to the high pressure source 49 so as to exert pressure upon the electrode 41. When operator 64 moved to the left, contactor II 9 closed thegap between the terminals .I I1 and H8, thereby sealing of? the foot switch I01 to prevent sequence interruption by switch I01. Simultaneously, contactor I32 on the operator 64 closes the gap between terminals I33 and I34, and a contactor I35 on operator 64 closes the gap between terminals I36 and I31. The terminal I33 is on one end of a line I38'ln weld time circuit I39, the other'end of which is connected to the negative potential line 69. The terminal I34 is connected to line I40 which is also connected to a cathode I4I of a controlledignition gas-filled discharge device as thyratron I42. One end of line I40 is connected through resistance I43 to the positive potential line 61 and the other end of line I40.is connected to the mid-point I44 of secondary I45 of a timing transformer I46. The secondary I45 is connected in parallel with a series-connected capacitance I41 and rectifying device I41 and two series resistances I46 and I49. Mid-points I50 and I5I of resulting voltage peaking grid-biasing circuit I52 are connected through a resistance I 53 to a shield grid I55 of the thyratron I42. Anode I56 of thyratron I 42 is connected by line I51 and resistance I58 to the positive potential line 61. Grid I59 of thyratron I42 is connected through resistance I60 to point I6I on one side of squeeze-time delay condenser I62 in the sequence initiating and squeeze-time delay circuit !25. The other side of condenser I62 is connected through current limiting resistance I65 to the point 68. The point I 6| on one side of condenser I62 isconnected through resistance I66 and potentiometer resistance I61 to the line 93 and through line I68 to anode I69 of a rectifying device I10 having a cathode I1I connected by line I 12 to point I13 on the voltage divider line 96. Because of the rectifying device I10, the point 16! will have a maximum positive potential approximately that of point I13 on the voltage divider line 96 fixed slightly positive with respect to line 69. Since the control grid I59 of thyratron I42 is connected through resistance I60 to the point I6I, the grid I59 will therefore be at a potential slightly positive with respect to negative potential line 69. When the potential first appeared across lines 61 and 69, the squeeze delay condenser I62 is charged with the side 68 positive with respect to the side I6I through the circuit consisting of line 61, resistance 83, inductance coil 68, point 68, resistance I65, squeeze-delay capacitance I62, point I6I, line I68, anode I69, cathode I1I, line I12, point I13, resistance I19 and negative potential line 69. At the moment that thyratron I21 started to conduct, the point 68 experienced a sudden drop in potential. Capacitance I62 being unable to-instantaneously discharge, the point I6I was forced far negative with respect to line 60. The control grid I59 of thyratron I42, being con;- nected to point I6I, was thereby correspondingly forced far negative with respect to line 69. Thus, even though operator 64 caused the negative potential of line 69 to appear at cathode I 4|, the thyratron nevertheless will not fire. Since the point I6I also became negative with respect to line I12, the rectifying device I10 ceased conducting and the squeeze-delay condenser I62 immediately began dischargingv through the cir-' cuit consisting of line 61, part ofresistance 95,

7 adjusting arm .94, line 93, potentiometer resistance I61, resistance I66, point I6I, squeeze-delay condenser I62, resistance I65, point 68., line I24, contactor I23, anode I26, cathode I28, line 86,,resistance Bland negative potentiol line 69. The rate of discharge of the squeezeedelay. condenser I62 is regulated primarily by potentiometer resistance I61.

,The action of squeeze-delay condenser I92 causes a potential picture at'the grid I59 of thyratron I42 shown in Fig.5 by a curve I59 in respectpto the potential at the cathode I4I shown by the curve I4I. After the condenser I62 discharges, it will tend to charge in the reverse direction so that grid I59 will become positive with respect to negative potential line '69. However. the positive potential at I6I is limited by the rectifying device I18 to the potential of point I13 on voltage dividerline 96 which is only slight- 1y, positive with respect to negative potential line. 69. When the point IISI reaches this slightly positive potential, the rectifying tube I19 will conduct and prevent further rise in potential. Even though this slightly positive potential at point I6I appears at the grid I59 so that the grid I59 is slightly positive with respect to the cathode I4I, the thyratron I42 will nevertheless still not conduct'because of the potential in the shield grid I55 caused by the peaking circuit I52. The potential at the shield grid I55 may be shown by the curve I55 in Fig. in which it is seen that the shield grid potential is maintained negative with respect to the cathode I II throughout most of a full cycle of. the alternating current souce I2. The alternating potential of the alternating current source I2 may-be shown by. curve E2 of Fig.5. The potential of shield grid I55 peaks to zero only once each cycle of the alternating potential from source I2. Therefore, even though grid I59 is, positive in respect to cathode II, the thyratron I42 cannot conduct until the shield grid I55 reaches a peak. The point at which this peak 'is reached with respect to the alternating potential from source I2 may be adjusted from aphasing circuit I15.

In one such suitable phasing circuit I15, a transformer secondary I15 of the transformer 29, whose primary 39 is connected across the alternatingcurrent source I2 by lines 3I and 32, is connected in series with a capacitance I11 and two potentiometer resistances I18 and I19, respectively. One end of the primary I 89 of peaking transformer I49 is connected at point I8I between the capacitance I11 and potentiometer resistance I18, and the other end of the primary I89 is connected to point I92 at the mid-point of the transformer secondary I19. By adjusting the resistance of potentiometers I18 and I19, the point at which the peaking circuit I52 will peak may be varied. A full explanation of the general operation of peaking circuitssuch as I52, may be found in the patent application of Dawson and Faulk, Serial No. 733,991 filed March 11, 1947, now Patent No. 2,569,720. The firing of 'thyratron I42 is, therefore, synchronized by peaking circuit, I52 with the alternating potential of source I2, and, in this instance, occurs at point I55 in curve I55 in Fig. 5.

As part of the weld time circuit I39, the line I51 in the anode I59 circuit or" thyratron I92 is connected by line I83 to one side of the parallel connected weld time condensers I84 and I85. The other side of condenser I64 is connected by line I85 through resistance I91, potentiometer resistance I 89 I and minimum timing resistance 8 I89 to the line 93. A'switch arm I90 is, in this instance. arranged to connect the side, IN 01 capacitance I to the line I86 so that capacitances I84 and I85 are in parallel and operate as a single enlarged capacitance, which is desirable in the present instance of pulsation welding. By moving the switch armto the point I92, the resistances I81 and I88 are shorted out and the capacitance I85 is disconnected from the circuit so that a resulting small time constant is achieved; which is desirable for spot-welding operation to be later described. For additional flexibility in varying breadth of weld time in pulsation welding, a further switch I93 may be providedforshunting outthe resistance at I81 along with adjustment of potentiometer resistance I88.

The weld time circuit I39 also inclues a heat time circuit'i95, acool time circuit I96 and a weld-triggering circuit I 91. In the heat time" circuit I95, a controlled ignition gas-filled .discharge 'device, as thyratron I99, having an'anode I99 connected by line 299' through resistance 291 to positive potential line 61, has a cathode 202 connected to line 293 which leads'through aresistance 294 totheline I83 leading to the anode of the thyratron 'I 42. A grid 295 of the thyratron I98 is. connected to a peaking circuit 296 similar to the peaking circuit I52 and having a transformer secondary 291 at the transformer I46. The peaking circuit 296 is arranged to produce a varying potential at the grid 295 shown by the curve 295"" in Fig. 5 wherein peaks occur mid way between the peaks of the 'curve I55. "The mid-point 289. of the transformer secondary 291 is connected to line 219, one end of which leads to the anode 2 II of a rectifying device 2 I2 whose cathode 2I3 is connected to line I12 which is connected to the point I13 which as stated is held slightly positive with respect to the negative potential line 69. The'other side of the line 2I9 is connected through minimum resistance 214 and potentiometer resistance 215 to the positive potential line 93. A switch 2I5 which is kept open for pulsation welding, as in the present instance, may be closed to shunt out thepotentiometer resistance M5 for spot-welding to be hereinafter described. Because of the rectifying device 2I2 connected by line 2I9 and point 208 to the grid 295, the potential of grid 295 will be slightly positive with respect to the cathode 292 of thyratron I98 when the thyratron I42 is conducting and the peaking circuit 296 reaches a peak. A timing capacitance 2I1- is connected between line 269, leadingfrom the anode I99 of the .thyratron I98, and line 2 I8, one end of which leads to an anode 2 I9 of the rectifying device 2 I2, and the other end of which is connected through a minimum resistance 22'9and av potentiometer resistance 22I. to the positive potential line 93,. The'line 2I8 is connected to mid-point. 222 of a transformer-secondary 223 of transformer I46 in a peaking circuit 224, sim'ilarto peaking circuit 'I'52,'which'is connected to bias grid 225 of a controlled-ignition gas-filled discharge device as thyratron 226 inthe cool time circuit I96. Anode 221 of therthyratron 228 is connected by line 229 throughresistance 229' to the positive potential'line 61. A snufiing capacitance 239 is connected between lines-228 and 299 for inverter operation of thyratrons 225 and I98. A timing capacitance 23I is connected between line 228 andline 2I9 leading to the control grid 265- of thyratron' I98:-

Two series-connected voltage dividerresistances-Brand 2.33 are" connected is at the same potential as line I86.

9 across. the anode 221 and cathode 234 of the thyratron 226. The cathode 234 is connected by line 235 to the negative potential line 69. A midpoint 236 between voltage divider resistances 232 and 233 is connected to a shield grid 231 of a controlled-ignition gas-filled discharge device 238, such as a thyratron, in the Weld triggering circuit I91. An anode 239 of the thyratron 238 is connected through the contactor I35 to one side of a primary 240 of a weld triggering transformer 31. The other side of the primary 248 is connected to the positive potential line 61. Grid 24I of the thyratron 238 is connected to a peaking circuit 242 similar to the peaking cir-' cuit I52 and having a secondary 243 of the transformer I46. Cathode 245 of the thyratron 238 is connected to line 246 which is connected by line 241 through resistance 248 to. the negative potential line 69. Line 246 is also connected to cathode 249 of a controlled-ignition gas-filled discharge device 258, such as a thyratron, in the weld triggering circuit I91. Grid 25I of thyratron 258 is controlled by a peaking circuit 252 similar to the peaking circuit I52 and having a transformer secondary 254 on transformer I46. The peaking circuit 252 has additionally a potentiometer resistance 253 for balance control to be hereinafter described. The mid-points of the transformer secondaries 254 and 243 are connected to the line 241 leading to cathodes 245 and 249. Anode 255 of the thyratron 250 is connected to the positive potential line 61 by line 256. A snuffing capacitance 251 is connected between the anode 255 of thyratron 250 and terminal I36 in the anode circuit of thyratron 238 for inverter operation of thyratrons 238 and 258.

Before the thyratron I42 fired, the weld time capacitances I84 and I85 chargedthrough the circuit consisting of positive potential line 61, resistance I58, line I83, condensers I84 and I85, point I9I, switch I98, line I86, line 258, anode 259, cathode I1I of rectifying device I10, line I12, point I13, resistance I14, to negative potential line 69. In this manner,'condensers I84, I85 charged with a potential positive in line I83 with respect to the line I86. Because of rectifying device I10, the potential of line I86 is normally maintained slightly positive with respect to the potential of line 69 and, therefore, grid 268 of a controlled-ignition gas-filled discharge device, as thyratron 26I, in a hold time circuit 262, However, since cathode 263 of thyratron 26I is connected by line 203, resistance 284, line I83, and resistance I58 to the positive potential line 61, the

cathode 263 will be positive with respect to the grid 268* when thyratron I42 is nonconductive and, therefore, the thyratron 26I cannot fire.

'When the thyratron I42 began to conduct current, as explained above, the potential of line I83 dropped to nearly the potential of negative line 69 thus putting voltage across thyratron 26!.

'However, the drop in potential in line I83, be-

cause of the charge on capacitors I84 and I85, simultaneously forces the potential of line I86 and, therefore, grid 260 far negative with respect to line I83 and, consequently, cathode 263 and, therefore, the thyratron 26I will still be unable to conduct. The potential of grid 269 with respect to line I83 may be shown by curve 266 with the line I83 potential shown by curve I83 in Fig. 5. The condensers I84 and I85 immediately begin to discharge through the circuit consisting of positive potential line 61, resistance 95,- potentiometer arm 94, line 93, resistance I89,

10 potentiometer resistance I88, resistance I81, line I86, capacitor I84, switch I90, point I9I, capacitor I85, line I83, line I51, anode I56, cathode I4I, point I34, contactor I32, point I33, line I38, and negative potential line 69. The rate at which the condensers I84 and I85 discharge is controlled primarily by potentiometer resistance I88 and resistance I81. 1

In the stand-by condition when potential first appeared across lines 61 and 69 and before the thyratron I42 began to conduct, the thyratron 226 being connected across the positive potential line 61 and the negative potential line 69 began to conduct as soon as its cathode became warm thereby charging the snuffing condenser 238 through the circuit composed of positive potential line 61, resistance 20I, line 208, snuffing condenser 238, line 228, thyratron 226, line 235, and negative potential line 69. The side 200 of snuffing condenser 238 is thereby charged positively with respect to the side 228. Timing condenser 2I1 is also charged through the circuit, line 61, resistance 29I, line 290, capacitance 2I1, line 2I8, rectifier 2I2, line I12, point I13, resistance I14, negative potential line 69, sothat the side 288 is positive with respect to the side 2I8.

The thyratron 250 being connected across potential lines 61 and 69 also began to conduct during stand-by when potential first appeared across lines 61 and 69. The snufi'ing condenser 251 is thereby charged during stand-by with its side I36, positive with respect to side 256. As soon as the thyratron I42 began to conduct, the drop in potential in line I83 immediately put potential across the anode I99 and cathode 202 of the thyratron I98 so that thyratron I98 i's'in condition to fire as soon as its grid 295 permits. Due to the peaking circuit 286, the potential at grid 205 shown by curve 205 in Fig. 5 peaks at point 205"" at the beginning of the half cycle of the alternating potential I2 following the half cycle in which firing point I55 of thyratron I42 occurred. Thyratron I98 thereby begins to conduct at the point 285 When the thyratron I98 begins to conduct, the potential of line 206 sud denly falls to nearly the potential of negative potential line 69 thereby causing the potential in line 228, due to the charge on condenser 238, to be forced far negative with respect to line 69 and shown by curves 228' and 69, respectively, in Fig. 5. The condenser 230 by this inverter action extinguishes the thyratron 226. At the same time, by similar inverter action effected by the biasing condenser 2 I 1, the potential in line 2 I8 is brought far negative with respect to the cathode 234 shown by the curves 2I8 and 234, respectively, in Fig. 5. The line 2 I8 being connected through the peaking circuit 224 to the grid 225 of the thyratron 226 will cause this low potential with respect to cathode 234 to appear at the grid 225. Thus, when the snuffing condenser 23!) discharges quickly and charges with the opposite polarity through the circuit consisting of positive potential line 61, resistance 229, line 228, snufling condenser 239, line 200, thyratron I98, resistance 28 4, line I83, thyratron I42, line 69, and a potential again appears across the thyratron 226, the negative potential at grid 225 prevents the thyratron 226 from again conducting. This is the start of heat time and the timing condenser 2I1 immediately begins to discharge through the circuit consisting of positive potential line 61, resistance 95, adjusting arm 94, line 93, potentiometer resistance 22I, resistance 220, line 2I8, timing condenser 2I1, line 200, anode I99, oath ode 292, resistance 294, line I83, line I51,'anode I55, cathode I4I,. point I34, contactor i32, point I33, line I38, and negative potential line 69. The rate at which the timing condenser 211 discharges is controlled primarily by potentiometer resistance 22! and determines the length of heat time." When the thyratron I98 began to conduct and the potential of line 2I8 was forced far negative, the rectifying device 212 stopped conducting. As the condenser 2 I1 discharges, it will have a tendency to reverse its polarity so that the side II8 will become positive with respect to the side 259. However, the positive potential at 2I8 is limited by the rectifying device 212 to the potential of point I13 on the voltage divider line 96.

As soon as thyratron 226 was extinguished, a potential appeared at 235 between the Voltage divider resistances 232 and 233. The resistances are chosen so that the potential at 236 will be the same as the potential appearing at the cathode 245 of the thyratron 238. Thus the shield grid 231 will be at the same potential and the thyratron 238 will be in condition to fire as soon as its grid 24I permits. terminals I36 and I31 when the operator 84 was forced to the left at the time of discharge of the squeeze initiating thyratron I21. Due to the peaking circuit 242, the potential at grid MI is made to appear with respect to cathode 245 as shown by curves 24I and 245 of Fig. with the position of peaks determined by the setting on phasing circuit I15. Thus, in the half cycle of the alternating line potential I2 immediately following the firing of thyratron I98, a peak 24I will occur at the grid of thyratron 2338 thereby causing it to fire. The moment thyratron 238 fires, it causes a sharp increase of current flow through the primary 240 as shown by the curve 249 in Fig. 5. This will, in turn, cause a voltage peak to occur in the secondaries 35 and 45 of the triggering transformer 31 shown by pulse 36 in Fig. 5. This pulse will overcome the negative bias at the thyratrons l5 and it caused by biasing circuits 21 and 40, respectively, so as to make a positive triggering pulse appear at the grids 25 and 38 thereby causing the thyratron with the proper polarity of line potential across it (in this instance 25) to conduct so as to ignite the ignitron I3 and make a pulse of current flow in the Welding circuit through. the weld load 49. The pulse of current may be shown by curve 43 in Fig. 5. 7

As soon as thyratron 233 is fired it causes, by

inverter action on snuffing capacitance 251, the 4 thyratron 255! to be extinguished. The potential in line 255 with respect to cathode 249 will appear as curves 255 and 246 in Fig. 5. The capacitance 251 rapidly discharges and recharges in the opposite direction through the circuit consisting of line 61, line 25 snuffing capacitance 251, point I35, contactor 535, point I31, anode 239, cathode 245, line 246, line 241, resistance 248 and negative line 59. When the capacitance 251 discharges, suitable firing potential will again appear across the thyratron 25;: so that the thyratron 259 will again fire as soon as the potential at grid 25! permits. The potential at the grid 25I with respect to cathode 249, due to the peaking circuit 252, may be shown by curves 25I and 246 in Fig. 5. Since the peaks at grid 25! are displaced in phase by 180 degrees from the peaks appearing at grid 24I of thyratron 238, the grid 25I will peak-in the succeeding negative half cycle of thealternating potential I2 at a point having the same relation as the point at A contactor I35 has closed the 25 which the thyratron 235 was caused to fire. The thyratron 255 will, therefore, be permitted tofire at this point 25I in the negative half cycle of alternating potential I2. When the thyratron 5 255 fires, it causes an inverter action on the snuff ing capacitor'251 thus forcing the potential at point I39 far negative with respect to cathode 245 (shown by curves I35 and 245 in Fig. 5) there.

by creating a potential drop across the transformer primary 248 in the same direction as the potential drop produced by the firing of the thyratron 233 and of about the same magnitude thereby causing an additional surgeof current through the transformer primary 253, shown at 249 on curve 243 in Fig. 5 which, in turn. causes a positive potential pulse to appear in the secondaries 36 and 45 of transformer 31, as shown by the curve 35'. This pulse overcomes the negative bias of the biasing circuits 21 and 49, as previously described, and triggers the thyratron I5 to conduct current to thereby ignite the ignitron I4 so as to cause a negative pulse of current to pass by means of transformer it through the welding load 49. The negative pulse of current may be shown by curve 49 and has the same magnitude and duration as the positive pulse 49 thereby providing proper balance and efficient operation of welding transformer Iii. To insure such proper balance the potentiometer resistance 253 in peaking circuit 252 has been provided. By adjusting potentiometer resistance 253 the po- .tential curve 25I" may be raised with respect to curve 246 thereby causing grid 25I to reach a proper firing potential at a point slightly before a peak is reached. Consequently thyratron 259 may be adjusted to fire at a point with respect to alternating potential [2 to exactly balance the point of firing of thyratron 233. The positive pulse appearing in the transformer secondary will have a small negative flare which will have no effect upon the operation of the thyratrons I5 and I6 since once the positive portion has caused conduction, current will continue to flow thereafter independently of grid potential. When, the thyratron 255 was again caused to conduct, it extinguished by inverter action of snuffing capacitor 251, the thyratron 239, which itself cannot again fire until its control grid 24! permits.

Assuming the line potential I2 to alternate in this instance at cycles per second, the thyratrons 259 and 238 may be made to alternately fire in the above manner in each successive half cycle thereby causing alternate positive and negative pulses of welding current to flow through the welding resistance 49. This alternate firing will continue until heat timing condenser 2" has timed out, as shown at point 2I8 in Fig. 5, and the peaking circuit 224 has produced a zero peak at the grid 225 of the thyratron 226, shownat point 225' in curve 22 5." illustrating the potential at grid 225. Thus, even though the condenser 2 I1 has discharged, the thyratron 226 cannot conduct except at the proper point in the cycle of alternating potential I2 determined by the M peaking circuit 224 which, in this instance, occurs at 225. Due to capacitance 2 I1 and peaking circuit 224, the potential at the grid 225 will appear as curve 225" and is normally coincident with curve 205. When the thyratron 226 again conducts at the point 22 5', it extinguishes the heat timing thyratron I98 by inverter action of the snufiing capacitance 239. The potential of line 200 with respect to line 89 and therefore cathode 202 appears as curves 290 and 69 in Fig. 5. By similar action, capacitance 23I forces the potenti'alat line 2| far negative with respect to potential of line 69 and appears through the peaking circuit 206 at the grid 205 of thyratron I98 as the drop 205. The cool time capacitance 23I immediately begins to discharge through the circuit consisting of positive potential line 61, potentiometer resistance 95, adjusting arm 94, line 93, potentiometer resistance 2 I5, resistance 2 I4, line 2I0, timing capacitance 23I, line 228, anode 221, cathode 234, line 235, and negative potential line 69. The rate at which the capacitance 23I discharges is controlled primarily by the potentiometer resistance 2 I 5. Before the thyratron I98 may again conduct, the capacitance 23I must discharge to point 205" and the peaking circuit 206 must have eiiected a peak at grid 205 after discharge of capacitance 23 I, in this instance shown by the point 205".

As soon as thyratron 226 began to conduct, the potential in line 228 dropped to nearly the negative potential of line 69 which, due to resistance 248, is lower than the potential at line 246. The shield grid 231 of the thyratron 238, being connected through point 236 and resistance 232 to line 228, will thereby have a correspondingly low potential. Thus, the shield grid 231 will prevent the thyratron 238 from further conduction. Thisnegative biasing potential on the shield grid 231 may be shown by curve 231 in Fig. 5. It is seen that when this biasing potential occurs in shield grid 231, if the thyratron 238 is conducting, it will continue to conduct until extinguished by the conduction of thyratron 250 after which it can no longer fire. If the thyratron 238 was already extinguished at the time the biasing potential in 231 occurred, it cannot again be triggered to conduct peaking circuit 242. Therefore, it is seen that the welding current during "heat time will always begin with a pulse of one polarity 49 and will always end with a pulse of the opposite polarity 4'9" with only an even number of current pulses occurring during heat time thereby equalizing the positive and negative pulses through the transformer I0.

After the cooling time determined by the discharge of condenser 23I and the peaking circuit 206, the thyratron I98 will again be made to conduct to repeat the cycle of heat and "cooling times explained above. While this repetitive action continues, the weld timingcapacitors I 84 and I85 discharge as shown by curve 260", thus 'efiecting the same potential at the grid 260 of the thyratron 261. It should be noted here that when the thyratron I 98 conducts, it

causes current to flow through the resistance 204 thereby effecting a potential rise in line 203. The resistance 204 is chosen so that the potential rise in line 203 will be of such a magnitude that the potential at the cathode 263 will be higher than the maximum possible positive potential at the grid 260 of thyratron 26I. The maximum positive potential at the grid 260 is determined by the line 258 which leads to the rectifying device I whose cathode is connected to the point I13 by line I12 on voltage divider line 96. Therefore, if the thyratron I98 is conducting, even though the capacitances I84 and I85 have timed out, the thyratron 26I cannot fire until the thyratron I98 is extinguished. The rise in potential of cathode 263 when the thyratron I98 conducts current through the' resistance 204 may be shown by curve 263' in Fig. 5, and in a similar manner, if thyratron I98 is extinguished and the thyratron 26I conducts, it causes current to flow through the resistance 204thereby-effecting a potential rise in the cathode 202 which is morepositive than the maximum possible positive potential in grid 205 thereby preventing the thyratron I96 from conducting after the thyratron 26I has started to conduct. Thus, if thyratron I98 is conducting when the weld time capacitances I84 and I85 time out, as in this instance shown by curve 260, the thyratron I62 will Wait until the thyratron I98 is extinguished by inverter action of thyratron 226 after which it will conduct at the point 263" thereby preventing the thyratron I98 from conducting thereafter. Note that this arrangement does not permit cutting short of any heat time period and insures an integral number of full heat time" periods.

The hold time circuit 262 has additionally a hold time capacitor 210 connected between lines 265 and 2H. One side of line 21I is connected through resistance 212 and potentiometer resistance 213 to the positive potential line 93, and the other side of line 21I is connected through resistance 214 to grid 215 of sequence terminating circuit 216. Line 21I is connected by line 211 to anode 218 of rectifying device 99 whose cathode I00 is connected to point I02 of the voltage divider line 96 thereby limiting the maximum positive potential at 21I to approximately that of the point I02 which is slightly positive with respect to line 203 when thyratron 26! is conducting. The other side of the capacitance 210 is connected by line 219 through resistance 269 to the line 28I, one end of which is connected to cathode 282 of the thyratron 2-83 and the other end of which is connected through capacitance 284 and line I06 to the point I04 between capacitor 88 and rectifying device 88 in the off time and repeat circuit 82. During stand-by, the capacitance 210 charges through the circuit consisting of positive potential line 61, line 266, capacitance 210, line 211, anode 218, cathode I00, point I02, resistance 285, point I13, resistance I14 andnegative potential line 69 so that the side 266 is positive with respect to the side 2'. When the thyratron 260 started to conduct, because of the charge on capacitor 210,

the line 21I was brought far negative with re spect to negative potential line 203, when thyratron 25I. is conducting, thereby producing at grid 215 the same negative potential. At the same time the cathode 282 is brought to the potential of line 266 in the anode circuit of thyratron 26I which is nearly at the negative potential of line 263 when thyratron 26I is conducting. Thus, the thyratron 216 is ready to conduct as soon as permitted by its grid 215. "Hold time" condenser 210 immediately starts to discharge through the circuit consisting of the positive potential line 61, resistance 95, adjusting arm 94, line 93, potentiometer resistance 213, resistance 212, line 21I, hold time capacitance 210, line 266, anode 265, cathode 263, line 203, resistance 204, line I83, line I51, anode I56, cathode I4I, point I34, contactor I32, point I33, line I38 and negative potential line 69. The rate of discharge is controlled primarily by the potentiometer resistance 213.

The potential picture at control grid 215 with respect to cathode 282 may be shown by the curves 215 and 282, respectively, in Fig. 5. When the control grid 215 reaches a potential slightly positive with respect to the cathode 282, the thyratron 283 will discharge so as to cause current to flow through the resistance 280 thereby effecting a potential rise in 28I which appears through capacitor 284 and line I06 to overcome the negative biasing potential at grid I05 of thy- 15 ratron"85' thereby causing thyratron 85' to fire. When.;thyratron 95 fires, capacitance 8| extinguishes thyratron I21by inverter action. At the same time grid-biasing capacitance 90 causes grid I29 to be forced far negative with respect to the potential of the cathode I28. Thus, while the snuffing capacitance 8I discharges rapidly because of a low'time constant, the capacitance 90 will prevent thyratron I21 from again firing. When thyratron I21 ceases to conduct, the coil 58 is deenergized and tension spring 85 moves the operator 64 to the right, thereby opening contacts at 93, I19, I32 and I35. By this action solenoid 51 is deenergized and pressure on electrode 41 is removed; conduction through thyratron I42 and cascaded thyratrons 281 and 283 is stopped;-terminals I35 and 131 are opened so as to insure against possible firing of thyratron 238.

' If the foot switch I01 is in the open position when thyratron I21 is extinguished so that terminals I98 and I09 are open, solenoid III is deenergized and tension spring I20 moves operator I20 to the left, opening line I24 and preventing "the thyratron i2! from further conducting and the ap aratus is again in position ready for another sequence, as explained above.

If foot switch I01 is in the closed position so that points I08 and I99 are closed, the solenoid III remains energized and the line I24 remains closed by contactor I23, and thyratron I21 will conduct to start another sequence, as explained above, when capacitance 99 has discharged through the circuit consisting of positive potential line 51, resistance 95, adjusting arm 94, line 93, potentiometer resistance 92, resistance 9I, repeat switch 89, line 89, off-time capacitor 90, line 84, anode 85, cathode 89, line 06, resistance 81, and negative potential line 69. The rate of discharge of off-time capacitor 99 is controlled primarily by potentiometer resistance 92.

If repeat switch 89 is switched to point 89" so that line 89 is open in front of resistance 9 I, and if the foot switch I91 is held in the closed position so that inductance coil III is energized leaving line I22 open, the off-time capacitor 90 cannot discharge, and therefore prevents the thyratron I21 from conductingindefinitely. By means of this feature, the repetition of the sequence may be prevented until the foot switch I01 is raised, thereby deenergizing the coil I i I and causing line I22 to close, and discharge off-time condenser 90 through the circuit consisting of line 84, line I22, contactor I2 I, point 89", switch 89, line 89, and condenser 99. The line I24 being open, thyratron I21 cannot again fire until the foot switch I81 is depressed.

The rectifying device 88 effectively prevents an unwanted phenomenon from occurring. For example, when the switch !01 is depressed and line I24 is closed, thyratron I21 fires and extinguishes thyratron 85. If the contactor I23 bounces, as contactors often do, the line I24 is momentarily open thereby causing the thyratron I21 to be extinguished. The biasing capacitance 90 has acquired suflicient charge through the line. 91 from rectifying device 99 to permit the thyratron I21 to refire when the bouncing contactor I23 again closes the line I25. However, if the rectifying device 88' were not present, the bias on grid I may have been lost during this small bouncing interval when both thyratrons I21 and ,85' were extinguished so that thyratron 85' may "refire thereby preventing the thyratron I21 from again refiring ,and' the sequence sticks until the l6 capacitance; 99- is again discharged, as explained above. By inserting the rectifying device" 94, loss of charge of biasing capacitance 93 is prevented thereby preventing the unwanted reiiring of thyratron and neutralizing the bouncing effect of contactor I23.

The above described apparatus may be used for spot-welding by moving the switch arm I to the terminal I92 and thus disconnecting the capacitance I85 and shunting out resistances I81 and I88. In such case, the capacitor I84 is discharged very rapidly. The thyratron 26| in the hold time circuit 262 thereby becomes ready to fire before the end of the first heat period and waits, as explained above, while the thyratron I98 is conducting. ,As soon as the thyratron I98 is extinguished at the end of the heat period, the thyratron 251 immediately conducts causing current to flow through resistance 204 so as to raise the cathode potential of thyratron I98 to a point where it cannot refire, as explained above.

Briefly summarizing, the sequence of operations described above is as follows:

1. Foot switch H31 is closed to energize solenoid III thereby moving operator I28 to the right.

2. The thyratron I21 in the sequence-initiating and squeeze delay circuit conducts and energizes the inductance coil 65 thereby moving the operator 54 to the left, at the same time extinguishing thyratron 85' in the off-time and repeat circuit '82.

3. The contactcr 53 causes solenoid 51 to be energized; contactor II9 seals in switch I01 to make the circuit non-beat; contactor I32 closes the cathode circuit of thyratron I42 in the weld time circuit I39; and contactor I35 closes the anode circuit of thyratron 238 in the triggering circuit I91.

4. After squeeze delay, thyratron I42 conducts starting weld interval timing and applying voltage to thyratron I93 in the heat time circuit I95.

5. Thyratron I98 conducts at zero voltage with respect to line at the-start of the half cycle following the one in which thyratron I42 started conduction. Thyratron I98 extinguishesthyratron 225 in the cool time circuit I95 which allows the shield grid potential in thyratron 238 to rise to-the same potential as its cathode 245, thus removing shield biasing from thyratron 23B.

6. At the proper point in the half cycle as determined by the phase shift heat control circuit I15, the thyratron 239 conducts, generating triggering voltage in the secondaries 36 and 45 of transformer 31, and at the same time extinguishing thyratron 258.

'1. Inthe next half cycle, thyratron 250 becomes condu-ctive at an identicalpoint in the half cycle as the thyratron 239 did in the preceding half cycle, and extinguishes the thyratron 238 and. causes another triggering pulse to appear in the secondaries '35 and 45 of transformer 31. This inverter action continues until the end of the first heat period.

8. At the end of the heat period, thyratron 226 again conducts, extinguishing thyratron I98 and returning biasing voltage to the shield grid 231 of thyratron 298 to stop the-inverter action of the triggering circuit I91.

9. At the end of cool time, thyratron I98 again conducts and the cycle repeats until th weld interval times out. i

10. The weld interval having timed out, if

during a cool time, thyratron 261 in the "hold time circuit 262 immediately conducts. If during a heat time, thyratron 261 waits until the end of the heat period and then conducts ending the weld interva and starting, hold time.

11. At the end of hold time, thyratron. 283, in the sequence-terminating circuit conducts and. pulses the grid of thyratron 85; which conducts and extinguish'es thyratron .I2'lwhich-per mits the operator 64 to move to the right:

12. If set for spot operation,- step 9 above is omitted and the thyratron 26I conducts imme-- 10 diately after. the end of thefirst heat. period.

Itshould be noted that by connecting the anode circuit of one: thyratron to the cathode circuit of a; succeeding thyratron, as illustrated bythy ratrons I42, 26Iand 283; a very: useful'cascade arrangement is obtained whereby the current howin the entire cascade arrangement .may be ex-=- tinguished from av single switch in the circuit ofthe leading thyratron thereby resetting the whole arrangement. Such an arrangementalso' permits the useof a simple resistance; as resistance 2%, in the cathode, circuits of succeeding thyratron's-for controlling the point of firing of'the' succeeding;

thyratrons; i V V Theinductance coil- (it-besides: controlling o'per' ator 64' is arranged to serve another'useful' pun pose. When' the thyratron I21 is extinguished; the currentin, the highly inductive: c'oil 66 is cut ofi rapidly. This causesi a:- rise 1 of: inductive volt age: in: the coil' whichv is kept: Within reasonable limits by resistance8'3 l This rise makespoint 6% highly positive and is in: series With lithe. circuit charging squeeze delay capacitance I62v which must be: completely recharged? duringv on time; Consequently, capacitance I621isrecharged very rapidlywith the resi'stancelfifi beinginserted to prevent overchargingt This isone of the factors contributing tothe high speeds obtainable in the. present invention; Forj example, in spot-- welding, 400 spots perminute may be, obtained. 5

The other timing capacitances have longer pe: riodsin whichto recharge; t

The unit: isself-compensating; fplf linje voltage variations; For example, the value; of ;charge' ol i a a en ma imQi QnQ hevoltage between line: 61 and; point p I I12 which is: afunction of voltagebetween; lines; {51; and 6 9 The discharge of capacitance 21)]; fer-timing de-r scribed above. is al'so a tuhctidnbt the voltage between. lines. 6']; and- 69;. Consequently, ir the line voltage is .low,,,the original charge on--capac i tance" 2707 is low,. but since' the discharging vo1tagewill'also'be'low, the same timing will res ulta g The potentiometer resistahceL5 is provided to, compensate, for? eirample,v for tolerances iniparts; by providing a slightvariation-inithe'discharge voltage. i 7

From the above" operational description it is"v noted that the technique of: driving} bothf grid and cathode of a th ratron negatives'imiiltaneously has been extensively u'sedi A" contribute; ing factor to the high stability. achieve'd in this" type, r operation is the; provision'offaj'capacit directly across the grid: andcathode in'ci'rcui which duringgstand-by, brinsgthefpositiye pct tia'lf of ii e 61" to the I cathode and harge these? capacitors so as to maintain the grid? rie with respect to the cathode. Such arrange maybeseen, forexa'mple inthyratronsflfl 2 and 283iwhere thecapa itorsreinam unnumbered."

In a second embodiment of the "presentT invenY- tion; the" portion- 290 iii Fig} 11 blocked in l n ie e ce ib 21 n'fiiZiOiwm S IE FQW: F"W 1@ 1g; e d? s uence t -merz Inthis embodiment, the'triggering circuit 29'-I re- 7 18 places the triggering and heat and cool time circuits I97, I and I96. In the triggering circuit 29I, controlled-ignition gas-filled discharge device 292, such as a thyratron, has anodev 293 connected by line 294 through resistance295' to the posi ive potential line segment ii'iwhich is connected to the rest of the positive potential line 647 at points a and b. Cathode 296 is connected through line 29? to the negative potential limit! at the pointe and grid 298 is connected to a grid biasing peaking circuit 299 which is preferably similar to the peak-ingcircuit I52. The secondary 365: of transformer Hit in the peaking circuit 29% has its midpoint tti connected to line 291 running to cathode 295. Point 302 in the output of the pea-king circuit 299m connected by line3il3 at the point d running to the shield grid I55 of thyratron itgin thev Weicltime circuit I39. Line 394 is inserted betweenpoints e and f, and line 305 is insertedbetween g and h to include the transformer secondary 28 in the grid-biasing circuit 27. A

controlled-ignition gas-filled discharge device 386,

such as-a thyratron has an anode 307 connected by means of points 308 and 309 and contactor 3H2 of operator 64 through a resistance 3I I to point i in the primary 2% of triggering transformer 37. Theother side of the primary 2 40 is connected at oint 1 to linefii. Cathode 3I2 is connected to thepoint3I3in1ine3I4.

The line3I4 is connected at pointk to line 263' running to cathode 263 of thyratron 72%| inthe"hold time circuit 262. The other end of 3I d runs to point 3I3 which is connec.ed through resistance 3H3, line 3H5, point 3H, and point 1 to the anodeIEfi of thyratron I42'in the weld time circuit i39; The anode I56is also'connected through resistance SIB to the positive potential line 6?; Grid 3119 of thyratron 356 is connected by line 323 to the output of peaking circuit 32! which is preferably similar to the peaking circuit 252 and has an adjusting potentiometer resistance 322- forraising and'lowering the output potential form of peaking circuit 32!. Mid point 323' of secondary 324 of transformer I48 is connected by line 325 through point 3I3 to cathode 3I2 of thyratron 306'. Point 326 inthe line 3H5 is connected by line 321 throughvthe point m' to shield grid i328 of the thyratron 26!. Point'329 of line 321 is connected through capacitance 336, resist- 0 ance 33I-, and=potentiometer resistance332 to the positive-potential line segment 93' whose ends are connected to the rest of line 93 at'poihts n ando. Point 333 between resistance 33! and capacitance 33D-is;connected.at the point p tovthe grid 25% timer is first turned 011;. the potential between lines-61;, and 69 appears across the thyratronetil in the triggering circuit'zti; becauseoflines 29 and- 2971 The thyratron zezwin, therefore, con-' duct during stand-by and will charge the condenser 33'!" with the point iteipositivewith respectto the line'29 l.

thyratron I i-2 will, nevertheless," be kept 'fronifir ing by the negative potential at its 'shield' grid from the peaking transformer 2 99, Whiclimay be When the conden er I $2 has timed? out, as shownat i551" iii-Fig; 6','t1-;e"

19 shown as curve'l'55 in Fig. 6. In the next half cycle of the alternating potential I2 after the squeeze-delay capacitor I62 has timed out, the peaking circuit 299 will produce a peak at a point I55 determined by a point selected by a setting on phasing circuit I thereby permitting thyratron I42 to fire. The weld time capacitance 330 had, during stand-by, charged through the circuit'consisting of line 61, resistance 3I8, point 3I1, line 3I6, point 326, line 321, point 329, capacitance 336, point 333, point p, line 258, anode 255, cathode Il'I, line I12, point I13, resistance I14, negative potential line 69 so that the side 329 is positive with respect to the side 333. The instant thyratron I42 is fired, because of the charge on capacitance 339, potential of point 333 and therefore grid 269 of thyratron 26! is forced far negative with respect to the potential in line 3I6 and cathode 263 so that thyratron 26I cannot fire, even though the firing of thyratron I42 created voltage across the thyratron L The potential of grid 266 with respect to line 3I6 is shown by curves 260 and 3I6 in Fig. 6. The weld timing condenser 336 immediately begins to discharge through the circuit consisting of line 61, resistance 95, adjusting arm 94, line 93, potentiometer resistance 332, resistance 33!, point 333, condenser 330, point 329, line 321, point 326, line 3I6, point 3I1, point Z, anode I56, cathode I4I, point I34, contactor I32, point I33, line I38, and negative potential line 69. The rate of discharge of the weld time condenser 336 is controlled primarily by the potentiometer resistance 332.

The firing of thyratron E42 with its consequent drop in potential of line 3I6 thereby also puts voltage across the thyratron 306. The points 309 and 368 have previously been closed by the contactor 3I6 of the operator 64 when induction coil 66 was energized. The thyratron 306 is, therefore, ready to fire as soon as permitted by the potentialof its grid 3 I9. The potential on the grid 3I9, due to the peaking circuit 32I, appears with respect to cathode 3I2 as curve 3I9 in Fig. 6 and has a phase relation causing peaks to occur 180 degrees from the peaks caused by the peaking circuit 299 shown by curve 298. Therefore, in the half cycle of line potential I2 following the firing of thyratron I42, the thyratron 306 will be permitted to fire, as at point 3I9'. The firing of thyratron 366 will extinguish, by inverter action of condenser 331, the thyratron 292. This action is shown by curve 264 showing potential of line 266 with respect to cathode 296. At the same time, a high current rise occurs in a transformer primary 240 thereby producing a positive peak in secondaries 36 and 45 of transformer 31 shown by curve 36. Due to the peaking circuit 299, the thyratron 292 will again be permitted to conduct at an identical point 298 in the next half cycle of alternating potential I2 thereby extinguishing the thyratron 238 and producing another positive peak 36' in transformer secondaries 36 and 45. The inverter operation of the triggering circuit 29I will continue to produce peaks in the positive and negative half cycles of the alternating potential source I2 to cause welding current pulses 49 through the load resistance 49, as explained with regard to triggering circuit I91 in the first embodiment, and will continue until thyratron 26I fires. When the capacitance 330 times out as at point 260, the thyratron 26! is ready to fire and will fire immediately if the thyratron 306 is extinguished thereby passing current through resistance 3I6 which raises the potential of cathode 3I2 above the maximum positive potential which may appear at the grid 3I9 so that thyratron 396 cannot thereafter fire. If the thyratron 306 is conducting at the time the capacitance 303 times out, as in the present instance, the thyratron 306 will cause current to flow through resistance 3I5 thereby raising the potential in line 3 I 4, shown by curve 3I4. Therefore, cathode 263 of thyratron 26I will be above the maximum positive potential that may appear at the grid 260, thereby making the thyratron 26I wait until the thyratron 306 is extinguished before the htyratrcn 26I is permitted to fire. By means of this feed-back arrangement through resistance 3I5, it is seen that only an even number of current pulses will be caused to flow in the welding transformer I6 and the operation will automatically be full cycling. The other operations in the sequence have been heretofore explained with regard to the first embodiment.

In a third embodiment, the invention forms a non-synchronous pulsation and spot-welding timer by removin the portion enclosed in the broken line 340 and inserting the portion 340 in Fig. 3. In this embodiment apulsation timing circuit MI is inserted in place of the triggering and pulsation circuits in the first embodiment. In the pulsation circuit 34I a cool time circuit 342 has a controlled-ignition gas-filled discharge device 343, such as a thyratron, having an anode 344 connected by line 345 throughresistance 346 to positive potential line segment 61 whose ends are connected to the rest of line 61 at points a and b. Cathode 348 is connected by line 349 to negative potential line segment 69 whose ends are connected to the rest of line 69 at points 0 and 20. Control grid 350 of thyratron 343 is connected through resistance 35I, line 352 and timing capacitance 353 to line 354. 'Line 352 is connected through resistance 355 and potentiometer resistance 356 to line segment 93 whose ends are connected to the rest of line 93 at point n and 0. Line 352 is also connected by line 351 to anode 358 of rectifying device 359 having a cathode 366 connected to line segment I12 the ends of which are connected to the rest of line I12 at points a: and :11. Anode 344 is also connected by line 345 through a snuffing capacitance 36I to line 354 leading to anode 362 of a grid-controlled gaseous discharge device 363 in a heat time circuit 364. The anode 362 is' connected through line 354, resistance 365 and solenoid coil 366 to positive potential line 61. Cathode 361 is connected to line 368, one end of which leads through point It to line 203 leading to cathode 263 of thyratron 26I in the hold time circuit 262. The other end of line 368 leads through resistance 369, line 310 and through point 1 to the anode I56 of thyratron I42 in the weld time circuit I39. Shield grid 31I of thyratron 363 is connected to point 312 in line 313 which is connected to line 314 leading from the line 310 to the shield grid-326 of thyratron 26I in the hold time circuit 262 through the point m. The point 312 is connected to one side of parallel condensers 315 and 316; the other side of condensers 315 and 316 may be connected in parallel by switch arm 311 to the line 318 leading to the point p in the grid 260 circuit of thyratron 26I. The line 318 is connected through resistance 319, potentiometer resistance 330, and minimum resistance 38I to the positive potential line 93. Resistances 380 and 319 may be shunted out by line 382,- point 383, and switch arm 311. The resistance 319 may be shuntedout by'con- :necting switch arm 384 to the point 385. Grid asmair 386 of thyratron 363 is. connected through reland potentiometer resistance 3.9.2 to line 93.. Also. line 398 is connected through line- 39.3 to anode.

394 of rectifying device 359. The. line: 395 is.in'- serted to connect points z and a. of; line 911:, the line 396 is inserted to connect the; point. b and c of line we and line 453 is inserted. to connect points a and h: of line 258. Any suitable con-- tactor 3.91, for connecting, alternating; current source I2 to the weld load 49:, is connected. by 1ine398 to the. point ct andby'linez399to poi-ntzef. The contactor 3.9.1. is controlled. at points: 43.91 and 40.! which may be: closed and opened by opera-tor 402 operated by the. solenoid. 3.6.6..

During stand-by, the potential betweenlines 61 and 69 appears across the thyratron. 343,. whose grid 356 being slightly positive in respect to its cathode 33, because of connection through rectifying device 359 to line I12, will make thyratron 343 normally conductive, The snufiingcondenser 36! will thereby be charged through the line 61, solenoid 366, resistance 365, point 354, snufiing condenser 36!, line 335, anode 344, cathode 3481, line 339 and negative potentialline 69 with the side 353 positive with respect to the side 345-. Because of rectifying device 359, line 389 and therefore grid- 363 of thyratron 363-wil1 be slightly positive with respect to line 39 during this stand-by conduction of thyratron 343. Also during stand-by, the condenser 353 in the heat time circuit 364 charges through the circuit consisting of positive potential line 61, inductance coil 366, resistance 365, line 354, capacitance 353, line 351, anode 358, cathode 369, line 112, point I13, resistance ift i. and anode potential line 63 so that the side, 35,3 is positive with respecsto the side 351'.

the circuit consistingof line 6.1 line. 3.13,, 1ine 314, line 3-13,: point 312, capacitances 3 15. and. 316, switch. arm 311, line 318, point p, line 2.58,.

sistance I13, andnegative potential line, 69. so that the point 312 is positive with respectto the,

line 318; During stand by, the positive potential of, line 61 appears at cathode 3610f thyratron- 363 in the heat time circuit 364through the; circuit fi'i, line 3.10,resistance 3.69, linev 3,69, cath ode 331 so that the-thyratron 363 willnot fire:

While thyratron I42. is non-conductive. The instant-the thyratron I42 fires, the. potential'in-line 31!). drops, thereby putting, voltage across. the

thyratron 35,3, and at the same't'ime, because. of capacitances 316and. 3.1.5., carries the potential at grid 269 for thyratron 26l inthe weldtime circuit 26.2 far negative-with respect. to line 316 and therefore cathode 2.63;. This may beseenin Fig. 7 by the curve 266 which represents thepotential of the grid 26!! and the curve 310 which ance 95, arm 94,,line 93, resistance 3'81, potentiometer resistance 383, resistance 319; line 318,

capacitances 315 and 316,1point 312', line 313', line 314, line 310, point Z, anode $56, cathode M1;

point I33, contactor i 32; point I33, line 138; and" negative potential line 69-. At theemoment that the potential in line 310 dropped," therebycans-- During stand-by, the weld time? interval condensers 315 and 316' charge. through heat time and startin @001 time",

22-. ing. voltage to appear across; the thyratron. 363,. the thyratron 363.conducts; When thyratron 363; conducts, it. causes current to; flow through the. inductance coil 366. so as: to: make the; operator 492 move upward,,;ther.eby closing: the gap" be.- tween the points: 30.0- and 4.0I'to operate; the contactor 391. so as topermit current. tov flow from. the alternatin current source. 42 through the weld load 43. At. the; instant the thyratron: 363 begins to conduct, it also causes, by inverter action of capacitance 361, the thyratron 33:4- to, be extinguished. The potential. picture in line; 3.45 leading to the anode 344. of. thyratron 343 is" shown by the: curve 345 in. Fig; '7. The potentialv there shown. is with respectto the potential at thecathode 343. shown. by the curve 343". Be.- cause of the charge on thevcap'acitanc'e 353;. explained: above, theinstant thyratron: 363- con ducts, the grid: 359 of the thyratron. 3.43: is forced far negative with respect to the cathode 3481,. as. shown by the curves 356- and 3.48,.respective1y', in Fig. 7.. Therefore, even though capacitance 3.6 I; rapidly discharges because of. a 10W time con-- stant, the capacitance 35.3 preventsthyratron343 from. again. firing unti1 the capacitance 353 has.

discharged to a point where the. grid 315.9: Willbe slightly positive with. respectto. the. cathode 348; The capacitancev 353 immediately begins to discharge through. the circuit; consisting of line 61,;

. resistance 95, adjusting arm 94, line: 93;..potentiometer. resistance-.356, resistance 355 line 3512, capacitance 353$, line13545,. anode 362; cathode-3:61,, line 368'; resistance-36.9,. line13i10;. point 1,. anode; I56, cathode I!3i,.pointi 1.34:,contactor I32, point 833; lineE38,.andnegative.potential-line-fifii. The

rectifying device 359rconnectedg to, theline 352:; prevents the capacitance: 353: from. recharging. in. the opposite direction beyondapiotentialslightly higher than negative. potential line; 69;. Thyra' tron 333 will; again conduct whencapacitance 353. discharges to. point 35.0" where the grid 3,59 becomes slightly positive.- withrespect to the p o tentialat cathode 398;. Whenthe thyratron 333 again fires, it extinguishes thyratron 363 by inverter action of. capacitance36i thereby ending Thepotential. in line 354 leading to; anode; 36% withre.- spect toline 3:1Bis shown by curves 35,4 and; 3.,16, respectively. When the. thyratron 343; fires; because cf the charge on; cool time? capacitance 389,. grid 38.6 of. thyratron 363 is-forced: far; nege ative with. respect toxthev potential of line 313. Cathode 3.61; being at the potential of line 313, thereby prevents refiringrofv thyratron 363,. even though capacitance. 361 has, rapidly discharged"v and recharged in they opposite direction; as at 33. 3. Current how will cease; in inductance coil 363 and operator, 332 will; drop'backto stopcurrent flow to thevveld load 49. The-resulting,potential.

picture of the control grid 3'86jissh0wnby curve 336? with; respect to potential. 316.. Thecool time condenser 389, immediately begins to che charge through the circuit: composed ot line 31',

resistance 95,- adjusting arm: 94, line 93, potentiometer resistance 392; resistance 39;! capaeig tance 339, line 333, line;..3.45, thyratron 3.3.3.;line:

339, and negative potentialline 69;.atca1rat'e, con;-. trolled primarily by the potentiometer resistance the cycle will berepeated. The cycle, as ex plained above, will continue to repeat until weld interval capacitors 315 and 316: time out ace-- cording to the curve 260 to. 260 where the' grid 260* of the hold' time thyratron 26 I2 becomes-z slightly positive with respect to cathode 263 and thyratron 26I may fire. If the weld interval capacitances 315 and 316 time out while thyratron 363 is firing, the thyratron 26I will, nevertheless, be unable to fire because current from thyratron 363 flowing through resistance 369 will cause cathode 263 to rise in potential to a pointabove the potential of control grid 266, as shown by the curve 263. Thyratron 26I will therefore wait until heat time ends and thyratron 363 is extinguished, at which time the thyratron 36I will immediately fire, thereby causing current to flow again in resistance 369 raising the potential of cathode 361 above the maximum possible positive potential of grid 386 so that thyratron 363 will be unable to fire again and the weld interval is ended. It is seen, as explained earlier, that this feed-back arrangement with the resistance 369 insures an integral number of full heat periods.

This embodiment is also adaptable to spotwelding, for example, by disconnecting capacitance 316 by means of switch 311 being connected to point 383, and also thereby shunting out resistances 386 and 319. The time constant is reduced to where capacitance 316 times out before the first heat cycle ends, thereby making thyratron 26I fire immediately after thyratron 363 is extinguished at the end of the first heat cycle.

In a fourth embodiment, the portion enclosed in dotted lines 346 is replaced by 465 of Fig. 4 to form a non-synchronous sequence spot-welding timer, In this embodiment, the weld time" capacitance 466 is charged during stand-by through the circuit consisting of line segment 61, which is connected at points a and b to the rest of line 61, inductance coil 461, resistance 468, line 469, capacitance 466, line 4I6, point p, line 258, rectifying device I16, line I12, point I13, resistance I14, and negative potential line 69 so that the charge at M6 is negative with respect to the charge at 469. When the capacitance I62 timesout, thyratron I42 fires, thereby causing the potential in line 469, which is attached at point Z to anode I56, to drop, thereby forcing the potential of the control grid 266 far negative with respect to cathode 263 as shown by the curves 266 and 263 in Fig. 8. Also current will be made to flow through the solenoid 461 so as to cause the operator 462 to close the gap between the points 466 and 46I thereby causing contactor 391 to connect a current source as, for example, source I2 through transformer I6 to the welding load 49. The capacitance 466 begins immediately to discharge through the circuit consisting of line 61, resistance 95, adjusting arm 94, line segment 93, which is connected at points n and o to the rest of line 93, potentiometer resistance 4, resistance 4l2, line 4I6, capacitance 466, line 469, point I, thyratron I42, point I34, contactor I32, point I33, line I38, and negative potential line 69. When the capacitance 466 discharges to the point 266 where grid 266 becomes slightly positive with respect to cathode 263, thyratron 26I discharges thereby causing current to fiow through the circuit, consisting of line 61, solenoid 4i3, line 4I4, resistance 4I5, point q, line 266, thyratron 26I, line 263, point k, line 469, point I, thyratron I42, point I34, contactor I32, point I33, line I38 and negative potential line 69. The current in solenoid 4I3 being in a direction opposite to that of solenoid 461 causes a neutralization of fields, thereby causing operator 462.120 fall back anddisconnect the points 466 24 and MI so as to end the 'weld interval. Line M5 is inserted to connect the points z and a of line 91; line M6 is inserted to connect the points I) and c of line I66; line M1 is inserted so as to connect the points a: and y of line I12; line M8 is inserted so as to connect the points c and w of line 69; line 4I9 is inserted to connect the points g and h of line 258; and line 426 is inserted to connect points d and a" to connect shield grid I55 to cathode MI. The rest of the circuit in this embodiment operates as discussed with regard to the first embodiment above.

This invention is not limited to the particular details of construction and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A timing system for use in supplying current through a load from a voltage source comprising means for controlling current from said source through said load, a pair of cascade connected controlled-ignition gas-filled discharge devices, means responsive to current fiow in the leading one of said discharge devices for causing said controlling means to conduct current through said load, means responsive to current flow in the other of said discharge devices for causing said controlling means to stop current fiow in said load, means for causing current to fiow in said one discharge device, time control means efiective only While said one discharge device is conductive for causing said other discharge device to conduct, and means for extinguishing said one discharge device thereby extinguishing said other discharge device.

2. A timing system for use in supplying current through a load from a voltage source comprising means for controlling current from said source through said load, a pair of cascade connected controlled-ignition gas-filled discharge devices, means responsive to currentfiow in the leading one of said discharge devices for causing said controlling means to conduct current through said load, said responsive means including an inductive device in the path of said current flow, means responsive to current flow in the other of said discharge devices for causing said controlling means to stop current flow in said load, said last-mentioned responsive means including an inductive device in the path of current of said other discharge device and positioned to nullify the field of said first-mentioned inductive device, means for causing current to flow in said one discharge device, time control means efiective only while saidone discharge device is conductive for causing said other discharge device to conduct, and means for extinguishing said one discharge device thereby extinguishing said other discharge device.

3. A timing system for use in supplying current through a load from a voltage source comprising means for controlling current from said source through said load, three cascade connected controlled-ignition gas-filled discharge devices, means responsive to current fiow in the first of said discharge devices for causing said controlling means to conduct current through said load, means responsive to current flow in the second of said discharge devices for causing said controlling means to stop current flow in said load, means for causing current to fiow in said first discharge device, time control means efiective 25 only while said first dischargedeviceis conductive for-causing said .second discharge device to conduct, timecontrol means effective only while :said second discharge device is conductive for causing the third of said discharge devices to conduct, and means responsive to current flow in said third discharge device for extinguishing said first discharge device thereby extinguishing said other discharge devices.

' 4. A timing system for use in supplying currentthrough a load from a voltage source comprising means for controlling current fromsaid sourcethrough said load, three cascade connected controlled-ignition gas-filled discharge devices, means responsive to current flow in the first of said discharge devices for causing said controlling means to conduct current through said load, means responsive to current flow in the second of said discharge devices for causing said controlling means tostop current flow in said load, meansfor causing current to flow in said first discharge device, time control means effective only while said first discharge device is conductive for causing said second-discharge device to conduct, and means responsive to-current flow in said third discharge device for opening the circuit of said first discharge device thereby extinguishing said-three discharge devices.

5. A timing system for use in supplying current through a load from a voltage source comprising means for controlling current from said source through said load, a pair of cascade con-- nected controlled-ignition gas-filled discharge devices, means responsive to current flow in the leading one of said discharge devices for causing said controlling means to conduct current through said load, means responsive to current flow in the other of said discharge devices for causing said controlling means to stop current flow in said load,means for causing current to flow in said one discharge device, a resistance capacitance circuit efiective only while said one discharge device is conductive for causing said other discharge device toconduct, and means for extinguishing said one discharge device thereby extinguishing said other discharge device.v

6. A timing system for use in supplying current through a load from a voltage source comprising means for controlling current from said source through said load, three cascade connected controlled-ignition gas-filled discharge devices, means responsive to current flow in the first of said discharge devices for causing said controlling means to conduct current throughsaid load, said responsive means including an inductive device in the path of said current flow, means responsive to current fiow in the second of said discharge devices for causing said controlling means tostop current flow in said load, said last-mentioned responsive means including" an inductive device in the path of current of said' other discharge device and. positioned to nullify the field of said first-mentioned inductive device, means for causing current to fiow in said first discharge device, a resistance capacitance circuit eiiective only While said one discharge device is conductive for causing said other discharge device to conduct, a resistance capacitance circuit eifective only while said seconddischarge device is conductive for causing the third of said discharge devices to conduct, and means responsive to current flow in said third discharge device for open-' ing the circuit of said first discharge device thereby-extinguishing said'thr'ee discliargedevice's; I

7. -A timing system for use in supplyingcurrent through a load from a voltage source comprising means for controlling current from said source through said load, three cascade connected controlled-ignition gas-filled discharge devices, means responsive to current flow in the first of said discharge devices for causing said controlling means to conduct current through said load, means responsive to current flow in the second of said discharge devices for causing said controlling means to stop current flow in said load, means for causing current to flow in said first discharge device, time control means efiective only while said first discharge device is conductive for causing said second discharge device to conduct, time control means effective "only while said second discharge device is conductive for causing the third of said discharge devices to conduct, an impedance in the path between said second and third discharge devices, and means responsive to voltage rise in said path from ourrent flow in said thirddischarge device for opening the circuit of said first discharge device vices.

8. A timing system for use in supplying current through a load from a voltage source com'- prising means for, controlling current from said source through said load, three controlled-ignition gas-filled discharge devices, one of said devices having each of the other two of said devices in cascade arrangement therewith, means responsive to current fiow in 'a 'second of said three devices for causing said controlling means to conduct current through said load, time con-' 'trol-means effective only while said one device is conductive for alternately making said second device conductive and nonconductive, means for causing said one device to conduct, time control means responsive to current flow in said one device for causing said third device to conduct,

a resistance between said one device and said sponsive to current flow in said third device for extinguishing said first device thereby extinguishing said three devices.

9. In a timing system, three controlled-ignition gas-filled discharge devices, one of said devices having each of the other two of said devices in cascade arrangement therewith, time control means efiective only while said one device is conductive for alternately making a second of said devices conductive and non-conductive, means for causing said one device to conduct, time control means responsive to current flow in said. one device for causing a third of said devices to conduct, a resistance between said one device and said other two devices in said cascade arrangement for making said time control means for said second device inefiective while said third deviceis conductive and said time control means for Said third'device ineffective while said second device is conductive, and time control means for extinguishing said first device thereby extinguishing said three devices.

10. In a timing system, a pair of cascade connected controlled-ignition gas-filled discharge devices, a resistance in the path between said leading one of said device's, time control means devices, means for causing current to flow in the

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